vested interest

Từ điển Oxford Advanced Learner 8th

ˌvested ˈinterest [vested interest] BrE NAmE noun ~ (in sth)
a personal reason for wanting sth to happen, especially because you get some advantage from it
•They have a vested interest in keeping the club as exclusive as possible.
•Vested interests (= people with a vested interest) are opposing the plan.
•She thinks that lawyers have a vested interest in making the legal process move slowly.